When host computers, which are communications terminals, perform data communications on a network, a router or a bridge as a relaying device retains communications route information and performs a communications control called routing, based on the communications route information thereof.
In this case, if, for example, a local area network (referred to as “LAN”) is divided into a plurality of areas, such as a factory, a warehouse, and a management department at a specific floor of a building, and a wired terminal (referred to as “host”) is disposed in each divided area (referred to as “segment”) but the segments cannot be connected each other via cables, the segments must be able to be connected to one another by using radio devices as relaying devices.
This enables the hosts in the segments to easily communicate with one another via the radio devices even if the hosts are too remote from one another to communicate via cables.
Further, in a case where the network is divided into a plurality of areas and communications are performed via the radio devices as described above, the hosts to communicate may be transferred into or out of the divided segments in accordance with a user's request. For example, when a product is manufactured or managed at a factory, there are cases where a host needs to communicate with other hosts in other areas while being moved by a cart. Since, in this case, the host is moved between each area, cable communications are difficult but wireless communications using radio devices are possible.
(Reference 1) Japanese Patent Laid-open Application No. 2003-18197
However, information (data) transferred between networks is packetized and controlled by TCP/IP that is conventionally used as a communication protocol.
For a router specifying a data transmission route established by TCP/IP or a bridge that merely performs a relaying function, data transmissions are controlled at a data link layer or a physical layer, which are arranged lower than TCP/IP that is a communications protocol.
A radio device (referred to as “radio bridging device”) having a bridging function used to connect between the divided segments must recognize, according to a destination of information (data) transmitted by a host in a segment where the radio device belongs, a product code (referred to as “MAC address”) of a terminal device that specifies a destination host of the data and address information (referred to as “IP address”) allocated to the terminal device on the LAN. Thus, upon a request of communications, the radio device connects the segments by selecting the MAC address of each host so that the source host and the destination host exchange information. Accordingly, information (data) can be certainly transmitted from the host in the segment to which the radio device belongs to a plurality of host including hosts in the other segments in accordance with a destination of the data.
Accordingly, information used for transmitting packet data between the segments on the LAN is usually recorded in a local table or a MAC table. If a radio device is used as a node for connecting the segments, it serves as a radio bridging device and retains the local table.
The address information and route information of each host recorded in the local table are preset by a LAN manager in a static manner if the number of hosts to exchange information is small and the hosts are not frequently transferred between networks.
However, when there are a large number of information terminals in the LAN, and elements of each host are easily changed such that the information terminal does not fixedly belong to a specific segment, destination route information is difficult to manage in the static manner as descried above. In this case, a dynamic routing scheme may be used to dynamically set the route information.
In a case where the dynamic routing scheme is applied to a wireless bridge that connects between the segments to transfer data, an address resolution protocol (ARP) request packet is broadcast at a specific timing. Thus, the IP and MAC address of each host belonging to each segment is acquired, and the addresses are stored together with a data route in a memory or the like.
However, the dynamic routing scheme has a drawback in that, since address information of each host on the LAN is regularly checked at a specific timing to search for route information, the hosts cannot exchange information while the route information is being searched for. Accordingly, the efficiency of transmitting information (traffic amount) on the LAN is degraded.
Further, in the dynamic scheme, the procedure is relatively complicated because a special packet obtained by processing data needs to be transferred. In addition, the address and route information of the host need to be stored all the time, thus laying a significant burden on a transmission device.